Women have been clued into the fact that their diets affect their fertility for a long while now, but a new study has found that what men are eating might matter just as much. The researchers found that the kinds of fat men ate made a difference in the quality of their sperm. For instance, saturated fat found in the dreaded bacon is no good, while the Omega-3s found in fish make for better swimmers.

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The study, which will be published in the journal Human Reproduction today, was led by Jill Attaman, who at the time was a research fellow at Massachusetts General Hospital and an instructor in Obstetrics, Gynecology and Reproductive Biology at Harvard Medical. (She is now an assistant professor at Dartmouth.) Attaman studied 99 American men being seen in a fertility clinic over a four-year period. The men filled out diet questionnaires and samples of their semen were taken and analyzed. Sounds like quite a way to spend an afternoon.

Researchers measured levels of fatty acids in the sperm, and in 23 of the men's samples, they also measured seminal plasma. Here's what the study found when it analyzed men according to the fat they consumed:

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The men were divided into three groups according to the amount of fats they consumed. Those in the third with the highest fat intake had a 43% lower total sperm count and 38% lower sperm concentration than men in the third with the lowest fat intake.

Though it wasn't just overall fat consumption that mattered; saturated fats were isolated as the real problem. And, interestingly, omega-3 fats were found to have a tiny positive effect on sperm production. Men who ate the most omega-3 fats had 1.9 percent more sperm that were formed correctly than men who had the lowest omega-3 intake. Wow, eat swimmers like fish (or at least down some fish oil), and your swimmers might be better. Sometimes nature really is magic.

Still, if you and your gentleman friend are trying to get pregnant, don't go too crazy and start tracking every bit of saturated fat that crosses your guy's lips. There are some serious limitations to this study, and it is by no means definitive proof that saturated fat leads to lousy semen. Instead, it is just a starting point. But it is a pretty good starting point. This is the first study to focus on dietary fats and male fertility, and, as Professor Attaman said, "The magnitude of the association is quite dramatic." Until further research can be done, she suggests,

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[I]f men make changes to their diets so as to reduce the amount of saturated fat they eat and increase their omega-3 intake, then this may not only improve their general health, but could improve their reproductive health too.

In other words, even if this isn't rock solid proof of causation, it probably can't hurt to infer some relationship between saturated fats and sperm quality—seeing as saturated fats have already been found to be bad for you in other ways, like giving you heart disease. Plus, we already know that bacon will kill you, and nothing makes you more infertile than being dead.